1. Field of the Invention
The present invention relates to a method for depositing a nanolaminate film consisting of first high-dielectric-constant layer/nickel oxide layer/second high-dielectric-constant layer, which is to be used in non-volatile floating gate memory devices, by atomic layer deposition (ALD), and to a non-volatile floating gate memory device comprising the same.
2. Description of the Prior Art
Memory devices, which have recently been increasingly used in mobile phones, MP3 players, digital cameras, USB devices, etc., are non-volatile memory devices that solve problems in the volatile operation mode of DRAM devices. As next-generation memory devices, non-volatile memory devices have received attention. The non-volatile memory devices include phase RAM (PRAM), polymer random access memory (PoRAM) devices, magnetic RAM (MRAM), and resistance RAM (RRAM), which use resistance switching or conductivity switching, as well as nano-floating gate memory (NFGM) devices.
Prior studies on non-volatile floating gate memory devices are broadly classified into two categories: the use of thin films, and the use of nanocrystals. Floating gate memory devices comprising thin films have a multilayer structure, such as a Si—SiO2—SiN—SiO2—Si (SONOS) structure or a metal-SiN—SiO2—Si structure. SONOS is now at the stage of practical application, but has a shortcoming in that the number of electron traps is small, leading to a reduction in the memory window width. For this reason, methods for inserting nanocrystals into high-dielectric-constant materials have been studied. With respect to this, studies on the use of silicon (Si) nanocrystals, germanium (Ge) nanocrystals, and tantalum nitride (TaN) nanocrystals have mainly been conducted (N. Takahashi et al., “Control of coulomb blockade oscillations in silicon single electron transistor using silicon nanocrystal floating gates,” Appl. Phys. Lett., 2000, 76, 209; M. Kanoun et al., “Electrical study of Ge-nanocrystal based metal-oxide semiconductor structures for p-type nonvolatile memory applications,” Appl. Phys. Lett., 2004, 84, 5079; A. Choi et al., “Highly thermally stable TiN nanocrystals as charge trapping sites for nonvolatile memory device applications,” Appl. Phys. Lett., 2005, 86, 123110). Recently, there have been reports of methods for inserting an Al metal into an Al2O3 film, and methods for inserting Ge crystals into an HfO2 film (S, Nakata et al., “Nonvolatile memory using Al2O3 film with an embedded Al-rich layer,” Appl. Phys. Lett., 2005, 87, 223110; S. Wang et al., “Investigation of Ge nanocrystals in a metal-insulator semiconductor structure with a HfO2/SiO2 stack as the tunnel dielectric,” Appl. Phys. Lett., 2005, 86, 113105). However, such methods employing nanocrystals have a problem in that nanocrystals, which play an important role in device characteristics, are difficult to form with uniform size and density over a large area. For this reason, floating gate memory devices comprising Al2O3 or Al-rich Al2O3 and floating gate memory devices comprising AlN or Al-rich AlN have been studied, and have been reported to have a high memory window compared to that of SONOS, and a low operating voltage compared to that of floating gate memory devices comprising nanocrystals.
Prior methods for making floating gates can be divided into physical vapor deposition and chemical vapor deposition, such as metal organic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD). In the physical vapor deposition, the surface of a grown thin film is rough, and it is not easy to grow a uniform thin film on a large-area substrate or a three-dimensional substrate, and it is more difficult to form a thin film than when using the chemical vapor deposition. Conversely, in the chemical vapor deposition, the roughness of a thin film is better, and it is easy to form a relatively uniform film on a large-area substrate, compared to the physical vapor deposition. In particular, the ALD adapted in the present invention is a method of depositing a thin film by alternately supplying a metal source and an oxygen source, in which, because a process can be carried out at lower temperature than MOCVD, a high-quality film can be deposited on a low-melting-point substrate such as glass, and it is very easy to control the thickness, even in the case of very thin films, and the surface roughness of a thin film is very small. Also, the ALD has advantages in that a thin film having uniform thickness can be formed either on a large-area substrate having a uniform composition or on a three-dimensional substrate having trenches or holes, and it is easy to dope different metals in desired amounts.
Meanwhile, a method of preparing aluminum oxide through the ALD method is a method of depositing a thin film by alternately supplying an aluminum source and an oxygen source. As aluminum sources, aluminum trichloride (AlCl3), trimethyl aluminum (Me3Al), triethyl aluminum (Et3Al), chlorodimethyl aluminum (Me2AlCl), aluminum ethoxide [Al(OEt)3], and aluminum isopropoxide [Al(OiPr)3], etc., have been reported [M. Leskela and M. Ritala, “ALD precursor chemistry: Evolution and future challenges,” J. Phys. IV 1999, 9, Pr8-837-Pr8-852].
Also, examples of a simple application of the ALD method for the deposition of a nickel oxide layer have recently been reported in several studies (M. Utriainen et al., “Studies of NiO thin film formation by atomic layer epitaxy,” Mater. Sci. Eng. B, 1998, 54, 98-103]; M. Utriainen et al., “Studies of metallic thin film growth in an atomic layer epitaxy reactor using M(acac)2 (M=Ni, Cu, Pt) precursors,” Appl. Surf. Sci., 2000, 157, 151-158). Nickel compounds known to be used in the prior ALD methods include several β-diketonate and β-ketoiminate compounds, such as (NiCl2), Ni(acac)2 (acac=acetylacetonato), Ni(tmhd)2 (tmhd=2,2,6,6-tetramethyl-3,5-heptanedionato), Ni(dmg)2 (dmg=dimethylglyoximato), and Ni(apo)2 (apo=2-amino-pent-2-en-4-onato) (M. Utriainen et al., “Studies of NiO thin film formation by atomic layer epitaxy,” Mater. Sci. Eng. B, 1998, 54, 98-103; M. Utriainen et al., “Studies of metallic thin film growth in an atomic layer epitaxy reactor using M(acac)2 (M=Ni, Cu, Pt) precursors,” Appl. Surf: Sci., 2000, 157, 151-158).
Meanwhile, the present inventors previously filed an invention relating to nickel aminoalkoxide compounds, represented by Ni[OCR1R2(CH2)mNR3R4]2 and useful as precursors for forming nickel oxide layers (Korean Patent Application No. 2003-0069585).
However, there is, so far, no example in which the NiO thin film grown using the ALD method is applied to non-volatile floating gate memory devices.